Correct, but you could formalise your answer a bit. It is possible that the momentum and force both have positive components in the x direction and have decreasing speed. The real issue is about the angle between the force and momentum vectors.

Correct, but you could formalise your answer a bit. It is possible that the momentum and force both have positive components in the x direction and have decreasing speed. The real issue is about the angle between the force and momentum vectors.

That makes sense, if the force was pointed straight down instead, would the ball's speed then be slowing down?